1. Field of the Invention
The present invention relates to an exhaust gas purification device, and more particularly to an exhaust gas purification device that purifies exhaust gas emitted from an internal combustion engine such as a gasoline engine.
2. Description of the Related Art
Generally, exhaust gas emitted from internal combustion engines contains, for instance, particulate matter (PM) having carbon as a main component, as well as ash made up of unburned components, and is known to give rise to air pollution. Regulations concerning emissions of particulate matter have become stricter year after year, alongside regulations on harmful components in exhaust gas such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). Various technologies for trapping and removing particulate matter from exhaust gas have therefore been proposed.
For instance, particulate filters for trapping such particulate matter are provided in the exhaust passage of internal combustion engines. In gasoline engine, for instance, a certain amount of particulate matter, though smaller than that in diesel engines, is emitted together with exhaust gas. A gasoline particulate filter (GPF) may accordingly be fitted in the exhaust passage. Such particulate filters include known filters having a structure, referred to as of wall flow type, in which a substrate is configured out of multiple cells made up of a porous substance, and in which the inlets and the outlets of the multiple cells are plugged alternately (Japanese Patent Application Publication No. 2009-82915 and Japanese Patent Application Publication No. 2007-185571). In a wall flow-type particulate filter, exhaust gas that flows in through cell inlets passes through a demarcated porous cell partition wall, and is discharged out through the cell outlets. As the exhaust gas passes through the porous cell partition wall, the particulate matter is trapped within the pores inside the partition wall. Prior art relating to such filters include WO 2003/068394, Japanese Patent Application Publication No. 2006-272288, Japanese Patent Application Publication No. 2012-236180, Japanese Patent Application Publication No. 2007-185571, Japanese Patent Application Publication No. 2009-663, Japanese Patent Application Publication No. 2013-43138 and Japanese Patent Application Publication No. 2013-139718.